The present invention relates to electronic volume control circuits, and more particularly to an electronic volume control circuit for controlling the level of an audio signal or the like in response to a digital signal.
A conventional device of this type is shown schematically in FIG. 1. As shown in FIG. 1, first terminals of an up switch 1 and a down switch 2 are connected to a power source +V.sub.DD, and second terminals thereof are grounded through resistors 3 and 4 and connected to respective input terminals of a two-input OR gate 5. The output of the OR gate 5 is applied to an AND gate 7 so that clock pulses produced by a clock pulse generator 6 pass through the AND gate 7. The clock pulses passing through the AND gate 7 are applied to an up-down counter 8, the up-down control of which is established by the output of the up switch 1.
The content of the counter 8 is applied as volume indicating data to a volume setting circuit 10 through a correction circuit 9. In the volume setting circuit 10, according to the applied volume data, an audio input signal is controlled in level.
When, for instance, the up switch 1 is depressed, the counter 8 receives clock pulses for the period that the up switch 1 remains depressed. In this case, the counter 8 performs an incrementing operation. Therefore, the number of clock pulses received is added to the present count value of the counter and the resultant count value is outputted as a digital signal. The digital signal is suitably corrected by the correction circuit 9 to provide volume data for the volume setting circuit 10.
With the above-described electronic volume control circuit, when the average level of the input signal changes, the available volume step sizes provided by the circuit may not allow for a comfortable listening level. More specifically, the electronic volume circuit is so designed that the volume step size is made small in the range of attenuation of -20 dB to -40 dB, which corresponds to an ordinary listening level for an ordinary input signal level, and is made large in other ranges. Accordingly, in the conventional circuit, the volume is controlled with a predetermined variation width irrespective of the magnitude of the input signal. Therefore, in the case where, for instance, because of a low level input signal, the electronic volume control circuit is used outside of the above ordinary range, the available step size for varying the volume becomes large, making it difficult to set the volume at a comfortable listening level.